🐐 Negation

centvrion/ast_nodes.py

@@ -330,6 +330,18 @@ class BinOp(Node):
         raise Exception(self.op)
 
 
+class UnaryMinus(Node):
+  def __init__(self, expr):
+    self.expr = expr
+
+  def __repr__(self):
+    return f"UnaryMinus({self.expr!r})"
+
+  def _eval(self, vtable):
+    vtable, val = self.expr.eval(vtable)
+    return vtable, ValInt(-val.value())
+
+
 class SiStatement(Node):
   def __init__(self, test, statements, else_part) -> None:
     self.test = test

centvrion/parser.py

@@ -14,7 +14,8 @@ class Parser():
         ('left', ["KEYWORD_ET"]),
         ('left', ["KEYWORD_PLVS", "KEYWORD_MINVS", "KEYWORD_EST"]),
         ('left', ["SYMBOL_PLUS", "SYMBOL_MINUS"]),
-        ('left', ["SYMBOL_TIMES", "SYMBOL_DIVIDE"])
+        ('left', ["SYMBOL_TIMES", "SYMBOL_DIVIDE"]),
+        ('right', ["UMINUS"]),
       ]
     )
 
@@ -173,6 +174,10 @@ class Parser():
     def binop(tokens):
       return ast_nodes.BinOp(tokens[0], tokens[2], tokens[1].name)
 
+    @self.pg.production('expression : SYMBOL_MINUS expression', precedence='UMINUS')
+    def unary_minus(tokens):
+      return ast_nodes.UnaryMinus(tokens[1])
+
     @self.pg.production('expression : KEYWORD_INVOCA id expressions')
     def invoca(tokens):
       return ast_nodes.Invoca(tokens[1], tokens[2])

tests.py

@@ -8,7 +8,7 @@ from centvrion.ast_nodes import (
   Bool, BinOp, BuiltIn, DataArray, DataRangeArray, Defini,
   Designa, DumStatement, Erumpe, ExpressionStatement, ID,
   Invoca, ModuleCall, Nullus, Numeral, PerStatement,
-  Program, Redi, SiStatement, String,
+  Program, Redi, SiStatement, String, UnaryMinus,
   num_to_int, int_to_num, make_string,
 )
 from centvrion.lexer import Lexer
@@ -105,6 +105,10 @@ arithmetic_tests = [
   ("X / III", None, ValInt(3)),           # integer division: 10 // 3 = 3
   ("II + III * IV", None, ValInt(14)),    # precedence: 2 + (3*4) = 14
   ("(II + III) * IV", None, ValInt(20)),  # parens: (2+3)*4 = 20
+  ("- III", None, ValInt(-3)),            # unary negation
+  ("- (II + III)", None, ValInt(-5)),     # unary negation of expression
+  ("- - II", None, ValInt(2)),            # double negation
+  ("III + - II", None, ValInt(1)),        # unary in binary context
 ]
 
 class TestArithmetic(unittest.TestCase):